Memory devices are typically provided as internal, semiconductor, integrated circuits and/or external removable devices in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), phase change random access-memory (PCRAM), and flash memory, among others.
Flash memory devices can be utilized as volatile and non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Uses for flash memory include memory for solid state drives (SSDs), personal computers, personal digital assistants (PDAs), digital cameras, cellular telephones, portable music players, e.g., MP3 players, and movie players, among other electronic devices. Data, such as program code, user data, and/or system data, such as a basic input/output system (BIOS), are typically stored in flash memory devices.
Two common types of flash memory array architectures are the “NAND” and “NOR” architectures, so called for the logical form in which the basic memory cell configuration of each is arranged. A NAND array architecture arranges its array of memory cells in a matrix such that the control gates of each memory cell in a “row” of the array are coupled to (and in some cases form) an access line, which is commonly referred to in the art as a “word line”. However each memory cell is not directly coupled to a data line (which is commonly referred to as a digit line, e.g., a bit line, in the art) by its drain. Instead, the memory cells of the array are coupled together in series, source to drain, between a common source and a data line, where the memory cells commonly coupled to a particular data line are referred to as a “column”.
Memory cells in a NAND array architecture can be programmed to a desired state. For example, electric charge can be placed on or removed from a charge storage node of a memory cell to put the cell into one of a number of programmed states. For example, a single level cell (SLC) can represent two states, e.g., 1 or 0. Flash memory cells can also store more than two states, e.g., 1111, 0111, 0011, 1011, 1001, 0001, 0101, 1101, 1100, 0100, 0000, 1000, 1010, 0010, 0110, and 1110. Such cells can be referred to as multilevel cells (MLCs). MLCs can allow the manufacture of higher density memories without increasing the number of memory cells since each cell can represent more than one digit, e.g., more than one bit. For example, a cell capable of representing four digits can have sixteen programmed states.
As flash memory cells in a flash memory device undergo programming, sensing, and erase cycles over the lifetime of the device, the accuracy and/or reliability of the cells may decrease, and a failure of the device may eventually occur. For example, after a particular point in the lifetime of the device, programming and/or sensing operations performed on the cells may not be accurate and/or reliable, resulting in a failure of the device.
A number of approaches can be used to monitor and/or anticipate the remaining lifetime of the device, e.g., the anticipated point at which the device may fail. For example, the number and/or duration of programming, sensing, and/or erase operations performed on the cells in the device can be tracked, e.g., counted, and an anticipated failure of the device can be indicated when the number and/or duration of programming, sensing, and/or erase operations performed on the cells reaches a particular quantity. These approaches, however, may not provide an accurate or reliable indication of the actual remaining lifetime of the device, because they may not account for variations in the storage and/or operating environment, e.g., temperature, of the device that can alter the remaining lifetime of the device.